Multi-cavity injection molding apparatus for making single or multi-layer molded container products are well-known. One or more types of molten material are typically injected into a cavity from a nozzle aligned with the center of the cavity to form the molded product. If more than one molten material is used for overmolding (i.e., molding one material over another material), the first material must cool and solidify sufficiently in the cavity before the second material can be injected over the first material. Once all the molten material in the cavity has cooled enough to solidify, the injection molding apparatus is usually opened to eject the molded product from the cavity. In order to properly cool and solidify, however, all of the molten material must remain in the cavity aligned with the nozzle for a relatively lengthy period of time before the injection molding apparatus can be opened. In the case of overmolding, this period of time can become quite lengthy due to the fact that each material must be sufficiently cooled and solidified before introducing another material. As a result, the injection molding apparatus has to wait this same amount of time before the cavity can be refilled with new molten material to form a new molded product. This arrangement causes the injection molding apparatus of the prior art to have relatively high cycle or production times, especially with respect to overmolding devices.
Multi-cavity injection molding apparatus for making multi-layer closures for containers or bottles are also well-known. A barrier layer of one material is typically molded within a closure layer of another material. The barrier layer molded within the closure layer, however, does not provide a direct seal between the closure and its respective container or bottle. For example, U.S. Pat. No. 5,094,603 to Gellert, entitled “Thermal Valve Gated Injection Molding Apparatus With Melt Distribution Plate,” issued on Mar. 10, 1992, commonly assigned with the present invention, and specifically incorporated in its entirety herein by reference, discloses a multi-cavity injection molding apparatus for making a two-layer closure with a barrier material molded within a closure material. While this invention has its advantages, since the barrier layer is formed within the closure layer, rather than adjacent to the closure layer's inner surface, an optimal direct seal is not provided between the closure and its respective container or bottle.
Injection molding of single-layer closures for containers or bottles is also well-known. To function properly, however, such closures usually require a second layer of a different material, namely a sealing layer. Typically, this sealing layer is a separate layer from the closure that is cut out of a sheet of sealing material and stamped or press-fit into a closure which was previously injection molded. These extra steps of cutting and stamping or press-fitting the sealing material, however, increase the time, labor, and cost involved with making the closure.
Alternatively, single-layer closures may be injection molded with an integral inner rim of the same material that helps provide a seal between the closure and its respective bottle or container. Adding the inner rim, however, involves using a more complex injection molding apparatus and process, thereby resulting in a more expensive closure. Moreover, the material used for the closure, and thus its inner rim, typically does not have as good of sealing ability as the sealing material used with the two separate layer closures described above.
Attempts have been made in the prior art to make closures with integral seal liner and shell components by injection molding a shell material over a seal liner material. An example of such an attempt is revealed in U.S. Pat. No. 4,803,031 to Ochs et al. Ochs et al. disclose an injection molding apparatus that utilizes two offset nozzles to inject sealing and shell materials into the same cavity chamber. In the Ochs et al. apparatus, the sealing material is injected from a first offset nozzle onto a mold core in a cavity chamber, and then cooled and solidified in the cavity chamber for a sufficient period of time. Next, the mold core of the Ochs et al. apparatus is dropped and backed away from the offset nozzles, and the shell material is injected from a second offset nozzle around and over the sealing material and mold core in the same cavity chamber to form the molded closure. The disadvantage of the Ochs et al. apparatus is that the seal liner and shell components are made in the same cavity chamber, one after the other, rather than simultaneously in separate cavity chambers. As a result of this design, the injection molding cycle or production times are greatly increased, thereby also increasing the time, labor, and cost associated with making closures.
Accordingly, it would be desirable to have an apparatus and method for injection molding that overcomes the problems associated with the prior art by implementing an efficient rotation or shuttling system between separate cavity chambers that reduces the overall cycle or production time for the products to be molded. In particular, it would be desirable to have an injection molding apparatus and method that allows for simultaneous molding of seal liner components and shell components over the seal liner components in separate cavity chambers to form integral, one-piece closures with improved sealing characteristics. In other words, it would be desirable to have an apparatus and method for injection molding a closure with an integral sealing layer, rather than the inner barrier layer, the separate sealing layer, or the inner rim taught by the prior art. Injection molding of a closure with an integral sealing layer would not only be relatively simpler and less expensive, but would also provide a closure with an improved seal between the closure and its respective bottle or container. It would also be desirable to use a rotation or shuttling system that can be readily implemented into standard injection molding apparatus, as opposed to specially designed injection molding apparatus.